A hush in the wood (3)
I believe the answer is:
ash
'wood' is the definition.
(wood from an ash tree)
'a hush' is the wordplay.
'hush' becomes 'sh' (both are used to tell someone to be quiet).
'a'+'sh'='ASH'
'in the' acts as a link.
(Other definitions for ash that I've seen before include "Tree; fire residue" , "Oleaceous tree" , "Tree; cinders" , "Fire's remains" , "What's left after burning" .)